Add error message for unhandled states and actions

asm.js

@@ -754,9 +754,15 @@ class Parser {
 	*handle(src) {
         let action;
 		for (const token of this.tokenizer.handle(src)) {
-            if (action = this.handlers[this.state](token)) {
+            const handler = this.handlers[this.state];
-                yield action;
+            if (handler == undefined) {
+                console.error(`ERROR: Unhandled state ${this.state}`);
+                this.state = State.TOP;
+                continue;
             }
+
+            if (action = handler(token))
+                yield action;
         }
 	}
 }
@@ -955,8 +961,13 @@ export class Assembler {
 
 	push(chunk) {
 		const text = this.decoder.decode(chunk, { stream: true });
-		for (const action of this.parser.handle(text))
+		for (const action of this.parser.handle(text)) {
-            this.handlers[action.type](action);
+            const handler = this.handlers[action.type];
+            if (handler == undefined)
+                console.error("ERROR: Unhandled action", action);
+            else
+                handler(action);
+        }
 	}
 
     lookup_block(symbol) {